Scientists have known for a while that humans seem to pick mates partly based on the way they smell. That's because a person's smell is related to their Major Histocompatibility Complex (MHC), a cluster of genes that shape a person's immune system. For years, scientists have debated whether people pick mates based on scent cues that indicate a potential mate has a very different MHC, which would give children a higher possibility of developing a robust immune system. And now a new study published in PLoS Genetics today shows that certain human populations are clearly following their noses to the wedding bed. The new study, conducted by a team of researchers from the UK, France, and China, used genomic analysis to determine at whether married couples were more likely to be "MHC-dissimilar." The results showed that European couples were overwhelmingly MHC-dissimilar, while African couples were neither similar nor dissimilar (in other words, they were just as likely to be similar as dissimilar). The researchers concluded that in the European population, mate selection may be driven more by biology than in other populations. Conclude the researchers in their paper:

At the molecular level, we found that the European American couples we studied are significantly more MHC-dissimilar than random pairs of individuals, and that this pattern of dissimilarity is extreme when compared to the rest of the genome, both globally and when broken into windows having the same length and recombination rate as the MHC . . . Such dissimilarity, observed from both molecular and serological data, cannot be explained by demographic processes, since such effects would affect the whole genome.

They're saying that the MHC-dissimilarity is not just caused by demographic factors like geographical location. Even more interesting was that the offspring of the MHC-dissimilar couples "were not more MHC-diverse than expected by random selection." So the marry-by-smell method may not actually be creating more robust offspring. More research is needed to discover why Europeans are more likely to marry for biological reasons than other populations are. Is Mate Choice in Humans MHC-Dependent? [via PLoS Genetics]